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The core structure of basal dislocations in deformed sapphire

IFF-News November 1, 2010

by Arthur H Heuer, Chunlin Jia, and K. Peter D. Lagerlöf

The atomic structure of dislocation cores is decisive for the understanding of plasticity in crystalline solids. The core structure of dislocations in sapphire introduced by high-temperature plastic deformation has been investigated with the use of the negative spherical-aberration imaging technique.

The ability of the above technique to discriminate oxygen columns from aluminum columns, combined with reproduction of subtle contrast features by image simulation, leads to a markedly detailed atomic model of the dislocation cores. The partial dislocations are found to be aluminium terminated, with electrical neutrality being achieved because half of the aluminium columns are missing. These partials also undergo core spreading, which results in random occupancy of both tetrahedrally and octahedrally coordinated sites, though aluminium in tetrahedral coordination never occurs in a perfect crystal. Unusual dislocation core structures may be present in other technologically important nonmetallic solids.